There are currently two main known types of objective method for determining the transmission quality of a coded speech signal on a communication link between a transmitter terminal and a receiver terminal: intrusive methods and non-intrusive methods.
Intrusive methods involve sending a reference signal from one extremity of the link close to the transmitter terminal and recording the degraded reference signal received at the other extremity of the link, close to the receiver terminal. The comparison between the reference signal and the degraded reference signal enables the quality of the transmission to be determined. Most commonly, the result of this determination is the attribution of a “mean opinion score” (MOS).
The quality measurement signals used in these intrusive methods overload the communication network and therefore need to be limited in number. Moreover, these signals are not real calls.
Non-intrusive methods involve measuring, at one point of the link, the data related to the coded speech signal sent between the transmitter terminal and the receiver terminal and attributing a quality score using this data.
A non-intrusive method is for example described in the document Malfait L., Berger J. and Kastner M., P. 563—The ITU-T Standard for Single-Ended Speech Quality Assessment, IEEE Transaction on Audio, Speech, and Language Processing, vol. 14(6), p. 1924-1934, (2006). This method is based on reconstituting the audio signal itself before degradation from the degraded audio signal sent and on the psychoacoustic models providing quality scores from the reconstituted audio signal.
However, this method is complex and requires a great deal of processing power. The complexity of this method prevents it from being used in all types of networks or terminals, and as such it is very rarely used.
A non-intrusive assessment method with no reference signal that is less complex and that requires less processing power is therefore required.